The present embodiments relate to medical diagnostic imaging. In particular, the left ventricle epicardium is estimated as part of medical diagnostic imaging.
Many cardiac interventions use real-time angiocardiogram imaging provided with a C-arm system. By rotating an X-ray source and detector on a C-arm, a 3D computed tomography (CT) volume may be reconstructed. C-arm CT has advantages compared to conventional CT. However, C-arm CT has challenges.
One specific challenge for the imaging of the heart is cardiac motion and respiratory motion. Electrocardiogram (ECG) gated CT reconstruction and breath holding compensate for motion and may be applied to C-arm CT. However, the X-ray source and detector typically sweeps the patient 5-6 times to capture enough 2D projection data for each cardiac phase. It is difficult for the patient to hold their breath during the whole procedure (e.g., during 30 seconds). Longer acquisition time may also incur more radiation dose.
It is desirable to reconstruct a CT volume with a single sweep of the C-arm X-ray source and detector. However, one rotation of a C-arm generates only about five 2D projections for each cardiac phase (e.g., about 130 2D projections with about 26 phases). Five 2D projections may be too few for adequate CT reconstruction. To make full use the projection data, the projections from different cardiac phases are aligned to the target phase in motion compensated reconstruction. Accurate estimation of the 3D motion from 2D rotational angiocardiogram is used to align to the target phase.
For this motion compensated reconstruction, the 3D motion for each voxel inside the volume is estimated. The motion may be estimated most easily for highly contrasted structures, such as heart chambers and aorta filled with contrast, and bones. However, accurate estimation of motion of some structure may be difficult. The motion of lowly contrasted structures, such as the epicardium of the left ventricle, may be difficult to estimate. The boundary contrast of the epicardium in an angiocardiogram is so low that even an expert may not be able to segment accurately. Rather than rely on possibly inaccurate detection of lowly contrasted structures, the motion for some voxels may be interpolated from the voxels associated with highly contrasted structures. However, interpolation may be an inaccurate approximation.